1. Field of the Invention
The present invention relates to a tire testing machine which as a single machine permits measurement of both uniformity and dynamic balance of a tire, as well as a tire testing method which permits measurement of both uniformity and dynamic balance of a tire in the tire testing machine as a single machine.
2. Description of the Related Art
Heretofore, as a tire testing machine capable of measuring both uniformity and dynamic balance of a tire, there has been known such a tire testing machine as shown in U.S. Pat. No. 6,131,455. The tire testing machine disclosed in the patent is provided with a spindle to hold a tire and a spindle housing which supports the spindle rotatably. At the side of the spindle housing is disposed a rotating drum having a rotational axis parallel to that of the spindle. In the rotating drum are provided load cells capable of detecting a load of double-axial component. In the spindle housing are provided fixing members for fixing (rigidly supporting) the spindle housing to a base against the load imposed from the rotating drum.
When measuring uniformity of a tire, it is necessary to bear the force applied from the rotating drum to the tire. For this reason the spindle housing is fixed to the base with the fixing members. The rotating drum is brought into contact with the tire and uniformity of the tire is measured from the load detected by the load cells.
On the other hand, when measuring dynamic balance of the tire, the fixing members are released to bring the spindle housing into a vibratable state and the spindle is rotated at a higher rotation speed than in the uniformity measurement. If a tire involving some trouble in dynamic balance is rotated at a high rotation speed, the tire rotates eccentrically and the spindle housing also rotates while deflecting with respect to the base. A load cell is disposed between the spindle housing and the base to measure a deflection of the spindle housing caused by the eccentric rotation of the tire, whereby dynamic balance is measured.
In the tire testing machine of the foregoing U.S. patent, the spindle fixing method in the dynamic balance test and that in the uniformity test are entirely different from each other, thus requiring the use of the aforesaid fixing members. Since it is necessary to fix the spindle housing which is heavy to the base, the fixing members are apt to become large in size and make the structure of the machine complicated. Besides, the testing time becomes long because it is necessary to perform the fixing operation with use of the fixing members. Moreover, since the fixing members engaging and disengaging operations are performed at every measurement, a difficulty has so far been encountered in point of reproducibility of the measurement.
In view of this point, there also has been known, for example, such a tire testing machine as is disclosed in U.S. Pat. No. 6,658,936. In this tire testing machine, as is shown in FIG. 2 of the U.S. patent, a fixing member is provided on an outer periphery surface of a spindle housing on the side opposite to a rotating drum, and with this fixing member, the spindle housing is rigidly supported by a base through triaxial piezoelectric force sensors.
In the tire testing machine of the U.S. Pat. No. 6,658,936, the triaxial piezoelectric force sensors are installed in the direction of a pressing force provided from the rotating drum at a distance corresponding to the outside radius of the spindle housing from the axis of a spindle. Therefore, if the load of a dynamic balance test or of a uniformity test is measured by the triaxial piezoelectric force sensors, a moment attributable to the distance is added as an error component to the measured load, thus contributing especially to a decrease of the balance evaluation accuracy.
In the tire testing machine of the U.S. Pat. No. 6,658,936 in question, since four triaxial piezoelectric force sensors are installed, it is difficult to effect positioning of a sensing direction.